1. Field of the Invention
The present invention relates generally to blinds and, more particularly, to a blind lift rod control lock for use in a blind assembly to lock the lift rod.
2. Description of the Related Art
A blind with hidden lift cord is known comprised of a headrail, a bottom rail, a set of blind slats, two lift cords, a frequency modulation mechanism, and a receiving mechanism. The frequency modulation mechanism and the receiving mechanism are installed in the headrail. The blind slats connected in parallel between the headrail and the bottom rail by ladder tapes. The lift cords each have one end connected to the receiving mechanism and the other end inserted through the blind slats and fastened to the bottom rail. The frequency modulation mechanism controls the tilting angle of the blind slats to regulate the amount of light passing through the blind. The receiving mechanism comprises a reversing spring, a lift rod, and two bobbins. The reversing spring is adapted to reverse the lift rod after the lift rod being rotated. The lift rod is rotated clockwise when the user lifting the bottom rail toward the headrail, or counter-clockwise when the user pulling the bottom rail downwards. The bobbins are fixedly mounted on the lift rod for synchronous rotation to roll up or let off the lift cords, for enabling the blind slats to be received or extended out. Normally, the reversing power of the reversing spring must be properly controlled. Excessive reversing power of the reversing spring may cause the lift rod to roll up the lift cords unexpectedly after the blind has been fully extended out, or may be unable to let the bottom rail be stopped at the desired elevation. Insufficient reversing power of the reversing spring causes the reversing spring unable to rotate the lift rod to the desired angular position when the user lifting the bottom rail of the blind. During lifting of the bottom rail by the lift cords, the reversing power of the reversing spring must conquer the gravity weight of the bottom rail and the weight of the blind slats being received at the bottom rail. Insufficient reversing power of the reversing spring cannot bear the total weight of the bottom rail and the blind slats, and the bottom rail may be stopped in position lower than the expected elevation. Therefore, the set value of the reversing power of the reversing spring determines the smoothness of the receiving or extending operation of the blind. Further, the reversing spring starts to wear quickly with use, resulting in an elastic fatigue. In order to prolong the service life of the reversing spring, the ends of the reversing spring may be made relatively wider or thicker. However, this improvement cannot completely eliminate the reversing spring from elastic fatigue.